1. Field of the Invention
This invention relates to photography and, more particularly, to a fluid spreading apparatus for use with a film unit of the self-processing type.
2. Description of the Prior Art
Fully automatic photographic systems for use with self-processable type films are well known in the photographic field and have been extensively described in the patent literature. These systems, such as Polaroid Corporation's "SX-70," are designed to automatically produce finished, waste-free photographs following their actuation. They accomplish this task through the use of a system architecture that generally comprises a group of specially designed interdependent function providing sub-systems that are organized to carry out a programmed series of sequential operations that ultimately result in the finished print. The order of operations, following system activation, usually begins with exposure of the film unit at some suitable predetermined location. Then the exposed film unit is advanced from the exposure location into engagement with a processing subsystem or apparatus. The function of the processing apparatus is generally twofold: to transport the film unit to the exterior of the system where it is accessible to the user and to spread a processing fluid across a selected photosensitive layer of the film unit during its transportation. The function of the processing fluid in this connection is to effect a diffusion transfer process that chemically transforms the latent image contained in the exposed photosensitive layer to a visible one, the final photographic image. It has been found that the quality of the final image generated by the diffusion transfer process is a critical function of the thickness distribution of the processing fluid over the photosensitive layer of the film unit. Consequently, the dominant concern in the design of every transport and processing system is to assure that the thickness distribution of the layer of processing fluid meets minimum requirements consistent with high quality of the final image. Naturally, this is achieved only through an understanding of all those parameters which may have an influence in processing performance.
In general, the present invention has this overriding concern but is particularly concerned with providing processing hardware solutions that are aimed at eliminating undesirable processing problems that can arise as a result of particular detailed interactions that take place between the film advancing subsystem, the processing apparatus, and the film unit during the transport and processing stage.
To be more specific, when the film unit is advanced from its exposure location in these fully automatic systems, it is usually advanced by a picking arrangement which engages its trailing edge on one side to provide a force to move it toward the processing apparatus. (See, e.g., U.S. Pat. No. 3,709,122). Because of the application of this asymmetric force, it has been observed that the film unit is engaged by the processing apparatus with its leading edge canted. Moreover, it has also been observed that it maintains this canted attitude throughout the processing stage. This canting is apparently the source of certain fluid coverage problems.
One of the problems that has been associated with the canting has been an incomplete coverage of the processing fluid over the picture area of the film unit. This has been particularly noticeable on the picking side near the corner of the read edge. It has been theorized that the canting may give rise to a lateral force component that causes the processing fluid to flow to the non-picking side. The prior art disclosed a remedy for this particular problem in the form of a processing roller having a reduced end diameter on the picking side. The reduced end diameter caused a reduction in the thickness of the processing fluid on the picking side so that its coverage capability was extended thereby eliminating the tendency toward incomplete corner coverage (see, e.g., U.S. Pat. No. 3,854,809).
Another problem associated with the canting has been an overall reduction in the thickness of the processing fluid layer near the picking side. This tendency is highly undesirable because of the requirement of thickness uniformity. And, in addition, the reduced end diameter roller solution seems inconsistent with eliminating this latter problem.
Because the one-sided picking arrangement is convenient for other reasons, the solution to both of these processing problems is preferably resolved by retaining the picking arrangement and looking elsewhere for a solution. There is, therefore, a need for a processing apparatus that can handle the canted film unit while eliminating the aforementioned processing problems.
The present invention approaches this problem by recognizing that the canting is the source of the problems but goes further by examining what can be done to influence the detailed interactions between the canted film unit and the processing apparatus to obviate these problems.